diff --git a/rgn2_replica/losses.py b/rgn2_replica/losses.py
new file mode 100644
index 0000000..ad1bbda
--- /dev/null
+++ b/rgn2_replica/losses.py
@@ -0,0 +1,54 @@
+import torch
+from torch import nn
+
+class AminoBretLoss(nn.Module):
+
+    def __init__(self, padding_token=-100, vocab_size=24):
+        super().__init__()
+        self.masked_loss = nn.CrossEntropyLoss(
+            ignore_index=padding_token, reduction="none"
+        )
+        self.chunk_perm_loss = nn.CrossEntropyLoss(reduction="none")
+        self.vocab_size = vocab_size
+
+    def forward(
+        self,
+        logit_out: torch.Tensor,
+        logit_chunk_perm: torch.Tensor,
+        target: torch.Tensor,
+        chunk_perm: torch.Tensor,
+    ):
+        """
+        logit_out:  bs, len, vocab_size
+        logit_chunk_perm: bs, 2 
+        target: bs, len
+        chunk_perm: (bs, 1)
+        """
+        global_petrub = 1 - chunk_perm
+
+        masked_lm_loss = (
+            self.masked_loss(logit_out.view(-1, self.vocab_size), target.view(-1))
+            .view(target.shape[0], -1)
+            .mean(1)
+        )
+
+        chunk_perm_loss = self.chunk_perm_loss(logit_chunk_perm, chunk_perm)
+        loss = (chunk_perm * chunk_perm_loss) + (1 - global_petrub * masked_lm_loss)
+
+        return loss.mean()
+    
+    
+"""
+vocab_size = 24
+bs = 20
+logit_out = torch.rand(bs, 10, vocab_size)
+logit_chunk_perm = torch.rand(bs, 2)
+target = torch.randint(1, 20, (bs, 10))
+chunk_perm = torch.randint(0, 2, (bs,))
+
+loss_func = AminoBretLoss(vocab_size=vocab_size)
+
+loss = loss_func(logit_out, logit_chunk_perm, target, chunk_perm)
+print(loss)
+
+"""
\ No newline at end of file
diff --git a/tests/test_loss.py b/tests/test_loss.py
new file mode 100644
index 0000000..38c52e1
--- /dev/null
+++ b/tests/test_loss.py
@@ -0,0 +1,16 @@
+from rgn2_replica.losses import AminoBretLoss
+import torch
+
+def test_aminobret_loss():
+    vocab_size = 24
+    bs = 20
+    logit_out = torch.rand(bs, 10, vocab_size)
+    logit_chunk_perm = torch.rand(bs, 2)
+    target = torch.randint(1, 20, (bs, 10))
+    chunk_perm = torch.randint(0, 2, (bs,))
+
+    loss_func = AminoBretLoss(vocab_size=vocab_size)
+
+    loss = loss_func(logit_out, logit_chunk_perm, target, chunk_perm)
+    assert True
+